<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button id="test">点击测试</button>
</body>

<script>

    document.getElementById("test").onclick = function(){  
        alert("点击测试");  
    };  
    
</script>
</html>